The title is a play on the musical "Hello Dolly!". Former cast member Victor Garber (Martin Stein) left the series in order to star in the Broadway revival of that musical.
Ray's new mustache is a parody of the infamous incident in the film Justice League (2017), where Henry Cavill's reshoots for the character of Superman were marred by the fact that a mustache he had grown for another part had to be (badly) removed via CGI. Brandon Routh (Ray) was Cavill's immediate predecessor in the role of Superman.
In Jewish mythology, a dybbuk is a malicious possessing spirit believed to be the dislocated soul of a dead person. It supposedly leaves the host body once it has accomplished its goal, sometimes after being helped.
The Emmy-nominated portrayal of Marie Laveau by actress Angela Bassett that Gideon mentions is a reference to Bassett's role in American Horror Story (2011).
The character of priestess Laveau is loosely based off the real-life Marie Laveau, a Louisiana Creole practitioner of voodoo from New Orleans, born in 1801 and died 1881 at the age of 80.